STAT6-mediated signaling in Th2-dependent allergic asthma: critical role for the development of eosinophilia, airway hyper-responsiveness and mucus hypersecretion, distinct from its role in Th2 differentiation.

When wild-type BALB/c mice were transferred with OVA-specific Th2 cells followed by OVA inhalation, a severe eosinophilia, mucus hypersecretion and airway hyper-responsiveness (AHR) was induced in parallel with a marked elevation of IL-4, IL-5 and IL-13 levels in bronchoalveolar lavage fluid (BALF). However, neither eosinophilia, AHR nor mucus hypersecretion was induced in Th2 cell-transferred STAT6-/- mice. The failure of eosinophilia was not due to the defect of Th2 cytokine production in BALF of STAT6-/- mice transferred with Th2 cells, but because of the defect of STAT6-dependent eotaxin production. Indeed, intranasal administration of eotaxin reconstituted pulmonary eosinophilia but not AHR and mucus hypersecretion in OVA-inhalated STAT6-/- mice. These results initially provided direct evidence that STAT6-dependent eotaxin production is essential for pulmonary eosinophilia. We also dissociated the role of STAT6 for eosinophilia from that for AHR and mucus hypersecretion. Thus, STAT6 also plays a critical role at late phase of Th2-dependent allergy induction.